In the prior art, a sensor for detecting a human body, e.g., an infrared sensor, etc., is traditionally stalled on a urinal to automate a task of rinsing the body of the urinal after usage thereof. Thus, a sensing window required to be exposed from the traditional infrared sensor may make against appearance and maintenance and also suffer from the following drawbacks.
On one hand, the traditional infrared sensor mainly adopts an active infrared sensing approach, that is, an infrared transmitter transmits infrared light at a wavelength, which is reflected by the human body and then received by an infrared receiver to determine the strength of the reflected signal, thereby achieving automatic sensing and determination. However, it may be rather difficult to achieve automatic sensing and determination for some substances with a low reflectivity in respect of infrared light (e.g., black clothing, hair, etc.). Only a small portion of infrared light from the infrared transmitter reflected by such substances can be received by the infrared receiver. The sensor can not determine whether there is a target object due to the insufficient strength of the reflected signal, which may result in a malfunction.
On the other hand, an amount of rinsing water will be discharged to rinse the urinal when the traditional infrared sensor detects again that a user goes away after a period of time since the user is detected. However, such a system for automatic rinsing dependent upon detection of presence or absence of the human body will discharge the amount of rinsing water regardless of whether it has been used by the user or of the amount of his urine, which may result in a considerable waste of water.
In the prior art, a conductivity sensor has been used to detect a variation of the conductivity of water at the location where a reservoir of a urinal is curved. Due to the difference between the conductivities of urine and tap water, an electrode of the conductivity sensor comes into contact with urine, if any, to detect a variation of the conductivity, so that an inflow of urine can be determined to thereby control rinsing of the urinal. The conductivity sensor addresses the drawbacks of the traditional infrared sensor that the sensing window has to be required and that it may fail to sense a substance with a low reflectivity.
Since a bathroom appliance, e.g., a urinal, etc., is typically powered by direct current (that is, powered by a battery), the phenomenon of polarization tends to occur with the electrode of the conductivity sensor. The so-called polarization refers to the departure of a potential of the electrode from its equilibrium value when (net) current flows therethrough, which is called polarization. The phenomenon that a potential of the electrode departs from an equilibrium potential of the electrode when current passes therethrough is referred to as polarization of the electrode. Thus, polarization of electrodes tends to cause inaccuracy of a conductivity detected between the electrodes, so that an actual condition may not be reflected properly, which may ultimately result in the problems of a degraded conductivity, a failure of sensing, etc.
Furthermore, a user may stand for a long period of time due to his prostatitis or another reason, so that the urinal arranged with the conductivity sensor will be rinsed in the case that the user has not gone away. This situation may discomfort the user on one hand and cause false determination of a failure of sensing of the urinal on the other hand. Still furthermore, a period of rinsing for the conductivity sensor has to be manually set, but the amount of rinsing water can not be determined dependent upon that of urine.
How to develop a more reliable conductivity sensor or a sensing device for a urinal using the same has become a common focus of attention in the industry.
Moreover, the conductivity sensor which has been widely applied in the field of a bathroom can be applied in other aspects than the sensing device for a urinal as described above, e.g., a water level detection device for a bathtub. The problem of polarization, a degraded conductivity or a failure of an electrode may also occur with the conductivity sensor, for example, applied as a water level detection device for a bathtub. Therefore, a more reliable conductivity sensor has also become a common focus of attention in the industry.